The present invention relates to a device for placement of a self-expanding endoprosthesis.
Endoprostheses are medical implants of generally tubular shape, made of metal or of polymer material and intended to keep open a channel which has a tendency to close under the effect of a disease (tumor, atheromatous plaque, etc.). This channel can, for example, be an artery, a vein, an airway, a urinary passage or a bile duct.
These implants are introduced in a contracted state so that they can be brought to the implantation site with the least possible trauma. They are then dilated to their final size either by plastic deformation or by their inherent resilience. Implants dilated to their final size by virtue of their inherent resilience constitute endoprostheses referred to as self-expanding, described for example by Hans Ivar Wallsten in patent FR 2 525 896.
These endoprostheses are put in place with the aid of a device consisting principally of:                an outer sheath which allows the endoprosthesis to be maintained in its compressed configuration. This sheath extends from its proximal end, which remains outside the body, to its distal end where the endoprosthesis is situated.        an inner mandrel which is of a length adapted to that of the sheath and slides inside the latter and, by means of a relative translation movement, allows the endoprosthesis to be pushed out of the sheath. This mandrel is joined temporarily to the endoprosthesis either by a fine layer of flexible material which adheres to the mandrel and in which the endoprosthesis will be embedded, the configuration described by John H. Burton et al. in the patent EP 0 408 245, or by an abutment which comes into contact with the endoprosthesis, as described by David J. Wilson et al. in the patent EP 1 025 813, or by other mechanical devices such as, for example, the one described by Brett W. Cryer in the patent WO 02/41805. This mandrel passes through the endoprosthesis and terminates in a flexible and rounded end which fits the end of the sheath and permits advance of the assembly during introduction without risk of damaging the tissues.        
In order to facilitate the travel of the instrument as it is advanced toward the zone to be treated, a guide wire is first introduced as far as this zone.
Two configurations are known:                the configuration referred to as coaxial, in which the mandrel is pierced from end to end to permit passage of the guide wire along its entire length.        the configuration referred to as “rapid exchange” described by Stephen R. Healy et al. in the patent EP 1 095 634. In this configuration, the mandrel has a passage between the distal end and a lateral opening situated a certain distance from this end. Instead of running through the whole device, the guide wire extends only along this short distance.        
To put the prosthesis in place, the practitioner first introduces the guide wire into the channel through and beyond the zone to be treated, then he introduces that end of the guide wire remaining outside the body into the distal part of the mandrel. He then slides it until it emerges either through the proximal end—coaxial configuration—or through the lateral opening—“rapid exchange”—then moves the device along this guide until the distal end is level with the zone to be treated, so as to position the endoprosthesis in line with the zone to be treated.
He then executes a relative translation movement between mandrel and sheath, which allows the endoprosthesis to emerge from the sheath. During this translation movement, he endeavors to keep the mandrel fixed relative to the channel while pulling back the sheath so that the endoprosthesis remains in line with the zone to be treated. When the endoprosthesis is entirely deployed, he can withdraw the device.
Correct positioning of the endoprosthesis is an indispensable factor in the success of the operation. To achieve this, it is absolutely essential to control the stability of the mandrel in its distal part throughout the deployment procedure.
To achieve this result, maneuvering grips have been proposed which permit a return movement of the sheath while maintaining the mandrel fixed in relation to the operating surgeon's hand. A device of this kind is described by Roy Sullivan in the U.S. Pat. No. 5,968,052.
The main failing of this type of instrument is that it cannot guarantee correct control of the movement of the distal part, particularly in cases where the instrument follows several curves inside the channels which lead it to the zone to be treated. The desired behavior of the instrument is such that the mandrel remains fixed in its distal part as in its proximal part and the sheath retreats in its distal part as in its proximal part. However, a different behavior may be caused by, for example, considerable friction between the outer face of the sheath and the wall of the channel to be treated. In this case, the movement of the sheath is correct at the proximal area, but it remains immobile in relation to the zone to be treated at its distal end, with the result that the compensation of the movement is effected by a modification of the curves of the instrument and it is the mandrel which, on leaving the sheath, is displaced relative to the channel to be treated.
This phenomenon is made still worse in cases where a moving organ is being treated, for example the coronary arteries.
It will be noted that placement of the endoprosthesis is often preceded by angioplasty intended to dilate the channel to be treated. This angioplasty is performed with the aid of a catheter comprising an angioplasty balloon made of a resistant and fairly inelastic material, so that it can be inflated to a defined diameter by means of a high pressure which can exceed 10 bar.
So as not to have to use two successive catheters, it has been proposed, especially in the patent application EP 0 699 451, to use an integrated catheter having, at its distal end, an angioplasty balloon and a means of deploying a self-expanding endoprosthesis. However, such a catheter does not solve the problem of positioning at the moment of placement of the endoprosthesis.
During deployment, the dilation balloon is situated downstream of the treated zone, that is to say in a healthy and much narrower channel. Because of the construction of the balloon, inflation, even at a very low pressure, causes dilation of the channel, which is a very unfavorable factor in terms of the phenomenon of restenosis. The patent application mentioned above indicates that the balloon remains deflated during deployment.
A catheter comprising a balloon of the angioplasty balloon type has also been proposed, in particular in the U.S. Pat. No. 6,030,413, for placing grafts held by staples. However, such a catheter is not suitable for placement of self-expanding endoprostheses.